RecyclerView.Adapter

This package is part of the
Android support library which
is no longer maintained.
The support library has been superseded by AndroidX
which is part of Jetpack.
We recommend using the AndroidX libraries in all new projects. You should also consider
migrating existing projects to AndroidX.

getItemViewType

Return the view type of the item at position for the purposes
of view recycling.

The default implementation of this method returns 0, making the assumption of
a single view type for the adapter. Unlike ListView adapters, types need not
be contiguous. Consider using id resources to uniquely identify item view types.

Parameters

position

int: position to query

Returns

int

integer value identifying the type of the view needed to represent the item at
position. Type codes need not be contiguous.

hasStableIds

Returns true if this adapter publishes a unique long value that can
act as a key for the item at a given position in the data set. If that item is relocated
in the data set, the ID returned for that item should be the same.

Returns

boolean

true if this adapter's items have stable IDs

notifyDataSetChanged

There are two different classes of data change events, item changes and structural
changes. Item changes are when a single item has its data updated but no positional
changes have occurred. Structural changes are when items are inserted, removed or moved
within the data set.

This event does not specify what about the data set has changed, forcing
any observers to assume that all existing items and structure may no longer be valid.
LayoutManagers will be forced to fully rebind and relayout all visible views.

RecyclerView will attempt to synthesize visible structural change events
for adapters that report that they have stable IDs when
this method is used. This can help for the purposes of animation and visual
object persistence but individual item views will still need to be rebound
and relaid out.

If you are writing an adapter it will always be more efficient to use the more
specific change events if you can. Rely on notifyDataSetChanged()
as a last resort.

notifyItemChanged

Notify any registered observers that the item at position has changed with
an optional payload object.

This is an item change event, not a structural change event. It indicates that any
reflection of the data at position is out of date and should be updated.
The item at position retains the same identity.

Client can optionally pass a payload for partial change. These payloads will be merged
and may be passed to adapter's onBindViewHolder(ViewHolder, int, List) if the
item is already represented by a ViewHolder and it will be rebound to the same
ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing
payloads on that item and prevent future payload until
onBindViewHolder(ViewHolder, int, List) is called. Adapter should not assume
that the payload will always be passed to onBindViewHolder(), e.g. when the view is not
attached, the payload will be simply dropped.

notifyItemChanged

Notify any registered observers that the item at position has changed.
Equivalent to calling notifyItemChanged(position, null);.

This is an item change event, not a structural change event. It indicates that any
reflection of the data at position is out of date and should be updated.
The item at position retains the same identity.

notifyItemRangeChanged

Notify any registered observers that the itemCount items starting at
position positionStart have changed. An optional payload can be
passed to each changed item.

This is an item change event, not a structural change event. It indicates that any
reflection of the data in the given position range is out of date and should be updated.
The items in the given range retain the same identity.

Client can optionally pass a payload for partial change. These payloads will be merged
and may be passed to adapter's onBindViewHolder(ViewHolder, int, List) if the
item is already represented by a ViewHolder and it will be rebound to the same
ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing
payloads on that item and prevent future payload until
onBindViewHolder(ViewHolder, int, List) is called. Adapter should not assume
that the payload will always be passed to onBindViewHolder(), e.g. when the view is not
attached, the payload will be simply dropped.

notifyItemRangeChanged

Notify any registered observers that the itemCount items starting at
position positionStart have changed.
Equivalent to calling notifyItemRangeChanged(position, itemCount, null);.

This is an item change event, not a structural change event. It indicates that
any reflection of the data in the given position range is out of date and should
be updated. The items in the given range retain the same identity.

notifyItemRangeInserted

Notify any registered observers that the currently reflected itemCount
items starting at positionStart have been newly inserted. The items
previously located at positionStart and beyond can now be found starting
at position positionStart + itemCount.

This is a structural change event. Representations of other existing items in the
data set are still considered up to date and will not be rebound, though their positions
may be altered.

notifyItemRangeRemoved

Notify any registered observers that the itemCount items previously
located at positionStart have been removed from the data set. The items
previously located at and after positionStart + itemCount may now be found
at oldPosition - itemCount.

This is a structural change event. Representations of other existing items in the data
set are still considered up to date and will not be rebound, though their positions
may be altered.

onBindViewHolder

Called by RecyclerView to display the data at the specified position. This method should
update the contents of the itemView to reflect the item at the given
position.

Note that unlike ListView, RecyclerView will not call this method
again if the position of the item changes in the data set unless the item itself is
invalidated or the new position cannot be determined. For this reason, you should only
use the position parameter while acquiring the related data item inside
this method and should not keep a copy of it. If you need the position of an item later
on (e.g. in a click listener), use getAdapterPosition() which will
have the updated adapter position.
Override onBindViewHolder(ViewHolder, int, List) instead if Adapter can
handle efficient partial bind.

Parameters

holder

VH: The ViewHolder which should be updated to represent the contents of the
item at the given position in the data set.

onBindViewHolder

Called by RecyclerView to display the data at the specified position. This method
should update the contents of the itemView to reflect the item at
the given position.

Note that unlike ListView, RecyclerView will not call this method
again if the position of the item changes in the data set unless the item itself is
invalidated or the new position cannot be determined. For this reason, you should only
use the position parameter while acquiring the related data item inside
this method and should not keep a copy of it. If you need the position of an item later
on (e.g. in a click listener), use getAdapterPosition() which will
have the updated adapter position.

Partial bind vs full bind:

The payloads parameter is a merge list from notifyItemChanged(int, Object) or
notifyItemRangeChanged(int, int, Object). If the payloads list is not empty,
the ViewHolder is currently bound to old data and Adapter may run an efficient partial
update using the payload info. If the payload is empty, Adapter must run a full bind.
Adapter should not assume that the payload passed in notify methods will be received by
onBindViewHolder(). For example when the view is not attached to the screen, the
payload in notifyItemChange() will be simply dropped.

Parameters

holder

VH: The ViewHolder which should be updated to represent the contents of the
item at the given position in the data set.

position

int: The position of the item within the adapter's data set.

payloads

List: A non-null list of merged payloads. Can be empty list if requires full
update.

onCreateViewHolder

This new ViewHolder should be constructed with a new View that can represent the items
of the given type. You can either create a new View manually or inflate it from an XML
layout file.

The new ViewHolder will be used to display items of the adapter using
onBindViewHolder(ViewHolder, int, List). Since it will be re-used to display
different items in the data set, it is a good idea to cache references to sub views of
the View to avoid unnecessary findViewById(int) calls.

Parameters

parent

ViewGroup: The ViewGroup into which the new View will be added after it is bound to
an adapter position.

onFailedToRecycleView

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled
due to its transient state. Upon receiving this callback, Adapter can clear the
animation(s) that effect the View's transient state and return true so that
the View can be recycled. Keep in mind that the View in question is already removed from
the RecyclerView.

In some cases, it is acceptable to recycle a View although it has transient state. Most
of the time, this is a case where the transient state will be cleared in
onBindViewHolder(ViewHolder, int) call when View is rebound to a new position.
For this reason, RecyclerView leaves the decision to the Adapter and uses the return
value of this method to decide whether the View should be recycled or not.

Note that when all animations are created by RecyclerView.ItemAnimator, you
should never receive this callback because RecyclerView keeps those Views as children
until their animations are complete. This callback is useful when children of the item
views create animations which may not be easy to implement using an RecyclerView.ItemAnimator.

You should never fix this issue by calling
holder.itemView.setHasTransientState(false); unless you've previously called
holder.itemView.setHasTransientState(true);. Each
View.setHasTransientState(true) call must be matched by a
View.setHasTransientState(false) call, otherwise, the state of the View
may become inconsistent. You should always prefer to end or cancel animations that are
triggering the transient state instead of handling it manually.

Parameters

holder

VH: The ViewHolder containing the View that could not be recycled due to its
transient state.

Returns

boolean

True if the View should be recycled, false otherwise. Note that if this method
returns true, RecyclerView will ignore the transient state of
the View and recycle it regardless. If this method returns false,
RecyclerView will check the View's transient state again before giving a final decision.
Default implementation returns false.

onViewAttachedToWindow

Called when a view created by this adapter has been attached to a window.

This can be used as a reasonable signal that the view is about to be seen
by the user. If the adapter previously freed any resources in
onViewDetachedFromWindow
those resources should be restored here.

Parameters

holder

VH: Holder of the view being attached

onViewDetachedFromWindow

Called when a view created by this adapter has been detached from its window.

Becoming detached from the window is not necessarily a permanent condition;
the consumer of an Adapter's views may choose to cache views offscreen while they
are not visible, attaching and detaching them as appropriate.

Parameters

holder

VH: Holder of the view being detached

onViewRecycled

A view is recycled when a RecyclerView.LayoutManager decides that it no longer
needs to be attached to its parent RecyclerView. This can be because it has
fallen out of visibility or a set of cached views represented by views still
attached to the parent RecyclerView. If an item view has large or expensive data
bound to it such as large bitmaps, this may be a good place to release those
resources.

RecyclerView calls this method right before clearing ViewHolder's internal data and
sending it to RecycledViewPool. This way, if ViewHolder was holding valid information
before being recycled, you can call getAdapterPosition() to get
its adapter position.

Parameters

holder

VH: The ViewHolder for the view being recycled

registerAdapterDataObserver

The adapter may publish a variety of events describing specific changes.
Not all adapters may support all change types and some may fall back to a generic
"something changed" event if more specific data is not available.

Components registering observers with an adapter are responsible for
unregistering those observers when finished.